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Tumors of the Peritoneum

Pathology

The peritoneum is a thin serous membrane that lines the inner surface of the abdominal cavity and envelops many abdominal organs, including the stomach, intestines, liver, and uterus. It serves to protect and support these organs, while also facilitating their smooth movement within the abdomen. Tumors of the peritoneum comprise a rare group of neoplasms that may arise as primary lesions or develop secondary to metastatic disease.

Types

Primary forms arise directly in the peritoneum and are less common. Among these, the most frequent are:

  • Peritoneal mesothelioma, which develops from mesothelial cells in the peritoneum;
  • Primary carcinoma of the peritoneum, a malignancy with histologic features similar to serous ovarian carcinoma, but developing independently of the ovaries.

Far more common are secondary forms, also referred to as peritoneal carcinosis, which result from the dissemination of malignant cells from primary tumors in other abdominal organs. The most frequent primary sites include the colorectum, ovaries, and stomach, with less common origins in the pancreas or liver.

Previously regarded as a terminal condition manageable only with palliative care, peritoneal carcinosis is now understood as a locoregional disease that, in carefully selected patients, may be amenable to multimodal treatment with curative intent. In this context, cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy (HIPEC) has emerged as one of the most innovative and promising therapeutic strategies.

The Numbers in Italy

According to data from the AIRTUM (Italian Association of Cancer Registries), primary tumors of the peritoneum are rare, representing less than 1% of all malignancies, whereas secondary involvement of the peritoneum is considerably more common, particularly in patients with advanced-stage abdominal cancers.

Risk Factors

Peritoneal tumors, whether primary or secondary, may be associated with a range of factors that increase the likelihood of involvement of the peritoneal membrane. The main recognized risk factors are summarized below:

  • Previous advanced abdominal malignancy: In particular, colorectal cancer, stomach cancer, ovarian cancer, or appendix cancer with a propensity for local spread are associated with a higher risk of developing peritoneal carcinosis.
  • Asbestos exposure: In cases of peritoneal mesothelioma, occupational or environmental exposure to asbestos is the principal known risk factor for this primary malignancy of the peritoneal lining.
  • Advanced age and female sex: Certain primary peritoneal tumors, particularly those histologically similar to ovarian carcinoma, occur more frequently in women over 60 years of age.
  • Genetic predisposition and family history: Germline mutations (e.g., in BRCA1, BRCA2, or genes associated with Lynch syndrome), as well as a family history of ovarian, fallopian tube, or peritoneal cancers, are associated with an increased risk of peritoneal neoplasms.
  • Obesity and hormonal factors: For some primary peritoneal tumors, obesity and a history of hormone replacement therapy have also been identified as associated risk factors.

Symptoms

In the early stages, tumors of the peritoneum may not show obvious signs of disease. In fact, symptoms often appear at a more advanced stage, when the tumor has spread within the peritoneal cavity.

The most common clinical manifestations include:

  • Ascites, defined as the accumulation of fluid within the abdominal cavity, leading to abdominal distension, bloating, and a sensation of tightness;
  • Progressive increase in abdominal circumference, not attributable to changes in diet or body weight;
  • Diffuse or persistent abdominal pain, often described as a feeling of heaviness or constant discomfort;
  • Alterations in bowel habits (alvus), such as constipation, diarrhea, or irregular bowel movements;
  • Dyspnea, resulting from diaphragmatic compression caused by the accumulation of ascitic fluid;
  • Anorexia and early satiety, related to compression of intra-abdominal organs.

Because these symptoms may also occur in a range of benign conditions, they should not be a cause for undue alarm. However, it is important to seek prompt medical evaluation if they are persistent or progressively worsening. A thorough clinical assessment enables the physician to determine whether further diagnostic investigations are warranted and, if a diagnosis is confirmed, to initiate an individualized treatment plan.

Diagnosis and Examination

The diagnosis of peritoneal tumors requires a careful, multidisciplinary approach, as clinical manifestations are often non-specific and may overlap with those of other abdominal conditions. The primary objectives are to detect the presence of disease at an early stage, evaluate its extent, and determine the most appropriate therapeutic strategy.

Level 1 examinations

The diagnostic work-up typically begins with a specialist clinical evaluation, followed by non-invasive imaging studies that are essential for detecting the presence of ascites or abdominal masses, including:

  • Abdominal ultrasound
  • Contrast-enhance CT scan of the abdomen and pelvis
  • Magnetic resonance imaging (MRI)
  • PET-CT

Second level examinations

When radiological findings suggest the presence of peritoneal disease, histological confirmation is required, meaning microscopic identification of tumor cells. This is obtained through:

  • Diagnostic paracentesis
  • Percutaneous or laparoscopic biopsy

Diagnostic Laparoscopy

In many cases, diagnostic laparoscopy represents a key step. It is a minimally invasive procedure that allows direct visualization of the peritoneal cavity, assessment of disease extent, and collection of tissue samples for histological examination. This procedure also helps determine tumor resectability, that is, whether the disease can be managed surgically.

Multidisciplinary Assessment

All diagnostic findings are reviewed within the Interdisciplinary Care Group (GIC) or Multidisciplinary Team (MDT). This multidisciplinary approach enables the development of a personalized treatment strategy, taking into account the biological characteristics of the tumor, the extent of disease, and the patient’s overall clinical condition.

Therapies

Once the diagnosis has been confirmed, the multidisciplinary team evaluates several factors in order to define an individualized treatment plan. Alongside the tumor type, size, and extent of disease spread, patient-related factors such as age, overall health status, and medical history are also taken into account. The proposed therapeutic strategy is then discussed with the patient, including alternative options when comparable efficacy is available.


For selected patients with particularly aggressive disease in whom standard treatments have not been effective, access to experimental therapies within clinical trials conducted by the Institute may also be considered. When deemed appropriate by the multidisciplinary team, this option is presented and carefully explained to the patient, with whom a shared decision-making process is undertaken.
Surgery

Surgery

The success of treatment for peritoneal carcinosis depends on careful patient selection, advanced surgical expertise, and appropriate postoperative management. These factors can be reliably ensured only in specialized referral centers dedicated to the treatment of this disease, such as our Institute.

Peritoneal Carcinosis

Over the past 20 years, the treatment of peritoneal carcinomatosis has made significant progress through the development of advanced surgical techniques and combined therapeutic strategies. This condition, once considered a terminal stage of disease, can now be approached in a targeted manner and, in selected cases, with curative intent.

The most effective and internationally recognized strategy is the combined approach, which includes:

  • Cytoreductive surgery, aimed at complete or near-complete removal of visible peritoneal disease
  • Intraperitoneal chemohyperthermia (HIPEC), which allows direct treatment of the abdominal cavity with heated chemotherapy agents.

Cytoreductive surgery

The objective of surgery is the removal of all macroscopic tumor implants within the peritoneal cavity. Since systemic chemotherapy penetrates only a few millimeters into tissue, complete surgical cytoreduction is a crucial component of treatment.

The procedure may include:

  • Removal of the primary tumor and regional lymph nodes
  • Resection of involved organs such as the spleen, gallbladder, portions of the stomach or intestine, and, in selected cases, the uterus and adnexa, depending on disease distribution.

When the disease involves the peritoneal lining, a peritonectomy may be performed, consisting of partial or total removal of the peritoneum (pelvic, parietal, central, or diaphragmatic), according to standardized and internationally recognized techniques. This approach is indicated only when a complete macroscopic cytoreduction can be achieved.

Intraperitoneal chemohyperthermia (HIPEC)

After completion of cytoreductive surgery, HIPEC is performed in the same operative session. During this procedure, the abdominal cavity is perfused for approximately 60–90 minutes with a chemotherapy solution heated to 41–42°C.

Hyperthermia enhances the cytotoxic effect of the drugs and acts directly on residual tumor cells, damaging their internal structures and reducing the risk of recurrence. Intraperitoneal delivery allows the administration of very high local drug concentrations, up to 1,000 times higher than systemic levels, while limiting systemic toxicity.

HIPEC is particularly indicated for tumors that predominantly remain confined to the abdominal cavity, such as ovarian, appendiceal, and primary peritoneal tumors.

Pseudomyxoma Peritonei (PMP)

Pseudomyxoma peritonei (PMP) is a rare mucinous neoplasm that most commonly originates from the appendix, and less frequently from other organs such as the ovary, colon, or small intestine. It is characterized by the progressive production and accumulation of mucin (gelatinous mucus) within the abdominal cavity, which can lead to increasing abdominal distension and, in advanced stages, impairment of organ function.

Historically, treatment was based on repeated debulking surgeries, aimed at partial removal of mucinous deposits and tumor masses. However, this approach provided limited long-term benefit, with frequent recurrences and poor survival outcomes, including 5-year survival rates of approximately 6% and perioperative mortality of around 2.7%.

Advances in surgical oncology have established the combination of cytoreductive surgery and intraperitoneal chemohyperthermia (HIPEC) as the current standard of care. This strategy, pioneered by U.S. surgeon Paul Sugarbaker, has significantly improved outcomes, with reported 10-year survival rates reaching up to 80% in carefully selected patients treated in specialized centers.

Management of PMP requires a high level of multidisciplinary expertise and should be performed exclusively in referral centers equipped with the necessary surgical experience and infrastructure to ensure both efficacy and patient safety.

Peritoneal Mesothelioma

Diffuse malignant peritoneal mesothelioma (DMPM) is a rare malignancy arising from the mesothelial cells that line the peritoneum, the thin membrane covering the inner surface of the abdominal cavity. It is strongly associated with prior exposure to asbestos and, in recent years, its incidence has shown a progressive increase, in parallel with pleural mesothelioma.

DMPM is generally poorly responsive to conventional systemic chemotherapy. However, in selected cases, systemic treatment may reduce tumor burden and render patients eligible for more radical surgical approaches.

As early as 2006, the Consensus Conference of the Peritoneal Surface Oncology Group International (PSOGI) identified the combination of cytoreductive surgery (CRS) and intraperitoneal chemohyperthermia (HIPEC), with or without systemic chemotherapy, as the standard of care for peritoneal mesothelioma.

Clinical outcomes with this multimodal strategy are significantly improved. Whereas median survival with systemic chemotherapy alone is approximately 12 months, combined treatment with CRS and HIPEC, with or without systemic therapy, has been associated with median survivals exceeding 50 months in specialized centers.

Peritoneal carcinosis of colorectal origin

Peritoneal carcinomatosis of colorectal origin may develop as a progression of colon or rectal cancer when malignant cells disseminate within the peritoneal cavity.

Thanks to advances in systemic therapies and the availability of combined treatment strategies, median survival for this condition has significantly improved, reaching approximately 24 months. These findings support the concept that peritoneal dissemination represents a biologically distinct pattern of metastatic disease compared with other forms of colorectal cancer spread.

In carefully selected patients, the combination of cytoreductive surgery (CRS) and intraperitoneal chemohyperthermia (HIPEC) has demonstrated further improved outcomes, with median survival approaching 30 months and a disease-free interval exceeding one year.

Based on this evidence, the Italian Association of Medical Oncology (AIOM) has included, since its 2016 guidelines, the option of CRS plus HIPEC for patients with isolated peritoneal carcinomatosis, provided that treatment is performed in specialized high-volume centers with dedicated multidisciplinary expertise in the management of this complex condition.

Peritoneal carcinosis of ovarian origin

Epithelial ovarian carcinoma is the most common and aggressive form of gynecologic malignancy. It is often referred to as a “silent tumor” because it typically causes few early symptoms and is frequently diagnosed at an advanced stage (III or IV), when peritoneal dissemination has already occurred.

Standard treatment for advanced ovarian cancer is based on two main pillars:

  • Cytoreductive surgery, aimed at removing as much visible disease as possible
  • Systemic chemotherapy, targeting residual microscopic cancer cells

The propensity of ovarian carcinoma to spread predominantly within the peritoneal cavity has made it a particularly suitable model for locoregional treatment strategies that act directly at the site of disease.

In this context, the combination of cytoreductive surgery (CRS) and intraperitoneal chemohyperthermia (HIPEC) has shown encouraging results. Initially adopted mainly in recurrent disease, this approach is now also considered in selected cases at the time of primary diagnosis, as supported by recent international evidence (Van Driel et al., New England Journal of Medicine, 2018).

This combined strategy, when applied in highly specialized centers and in appropriately selected patients, can significantly improve overall survival and quality of life, offering new therapeutic perspectives even in advanced stages of the disease.

Chemotherapy

The treatment of peritoneal carcinosis is increasingly based on a multimodal approach that combines different therapeutic strategies to optimize patient outcomes.

Within this framework, systemic chemotherapy may be administered:

  • Before surgery (neoadjuvant setting), to reduce tumor burden and increase the likelihood of achieving complete cytoreductive surgery;
  • After surgery (adjuvant setting), to reduce the risk of recurrence and limit disease dissemination beyond the peritoneal cavity.

In recent years, the development of more targeted and effective agents has contributed to improved treatment outcomes and has enabled a more personalized therapeutic approach. However, standardized protocols regarding the number of cycles, timing, and drug combinations are still lacking, as management must be tailored to the individual patient.

For this reason, it is essential that each patient be managed within an Interdisciplinary Care Group (ICG) dedicated to this disease. This multidisciplinary team, composed of oncologists, surgeons, radiation oncologists, and other specialists, collectively evaluates the clinical situation, defines an individualized treatment plan, and accompanies the patient throughout the entire therapeutic pathway.

Supportive Therapies

Patients with peritoneal carcinosis receive comprehensive support throughout their diagnostic and therapeutic journey from specialists in palliative care, nutrition, and psycho-oncology.

Ongoing Support

At the Candiolo Cancer Institute, physicians and nurses within the multidisciplinary team are available to provide patients with comprehensive support in managing the various side effects that may arise during treatment.

Direct line to specialists

The cancer patient is often a vulnerable individual who requires continuous support throughout the disease course. When new symptoms arise, whether related to the underlying disease or to treatment-related adverse effects, it is essential that timely specialist evaluation is ensured through a dedicated “fast track” pathway.

The Candiolo Cancer Institute provides a dedicated support service, available Monday to Friday from 8:00 a.m. to 5:00 p.m. Patients may contact the Oncology Day Hospital Secretariat at +39 011.993.3775 to report the need for an urgent clinical assessment. The referring specialist is then promptly informed and will contact the patient to ensure timely evaluation and appropriate management.

Continuing care and palliative care

At the Candiolo Cancer Institute, multidisciplinary specialists are available to provide patients, when needed or upon request, with comprehensive supportive care, including:

    • nutritional support

    • psychological support

    • physiotherapy

    • dressing of venous access devices

    • pain therapy

    • Management of other coexisting conditions.

Social work

Social work

The Social Service Department of the Candiolo Institute conducts information and orientation interviews for patients and their families on how to access services in the area and how to obtain welfare and social security benefits provided by law (disability, benefits for aids and prostheses, work leave, etc.).

The service operates on Wednesdays and Fridays from 9 a.m. to 1 p.m. – Phone: 011.993.30

Follow up

At the end of the treatment course, the follow-up phase begins. During this period, clinical evaluations and diagnostic tests are performed to monitor treatment-related side effects, assess therapeutic efficacy, and evaluate the patient’s functional recovery.

Follow-up is essential for the early detection of disease recurrence, enabling timely initiation of appropriate therapeutic strategies. It also provides an important opportunity for ongoing communication between the patient and the treating specialist.

Follow-up visits are scheduled by the same specialist physician, who assesses the patient’s clinical status and reviews the results of the required investigations.

Surveillance is typically conducted at predefined intervals over a period of 5–10 years and may include clinical examination, blood tests, tumor markers (CEA and CA 19-9), and contrast-enhanced computed tomography (CT) scans of the chest and abdomen.

Initially, follow-up is more frequent, generally every three to six months, and is then progressively spaced out over time, eventually transitioning to annual assessments. The frequency and type of investigations are individualized according to tumor stage and treatments received.

Interdisciplinary Group

Every cancer requires, at all stages of its management, a multidisciplinary approach, which at the Candiolo Cancer Institute is ensured by a team of specialists from the various clinical and surgical departments. This team is referred to as the GIC (Interdisciplinary Care Group).

The GIC is responsible for accompanying each patient throughout the entire diagnostic and therapeutic pathway, including the prescription and scheduling of examinations, as well as communication with the patient and their family members. It defines and shares a personalized care plan for each individual, based not only on the type and stage of the tumor but also on patient-specific characteristics. The objective is to achieve the best possible oncological and functional outcomes while maintaining an optimal quality of life.

The Group also collaborates closely with the Institute’s research teams to ensure timely access to the most recent innovations in screening, diagnosis, and treatment arising from ongoing scientific research.

Clinical Divisions

The diagnostic and therapeutic pathway for peritoneal tumors at the Candiolo Cancer Institute involves several clinical divisions, including:

Why Choose Us

At the Candiolo Cancer Institute, each patient with pancreatic cancer is managed through a highly specialized approach, supported by the coordinated work of a dedicated Interdisciplinary Care Group (GIC).

Clinical experience and tailored approach

Due to the high number of cases treated each year, the Candiolo Institute is a national reference for taking pancreatic cancers. Our experience enables us to deal with even the most complex situations, always with a personalized approach built on the clinical and personal profile of each patient.

Imaging technologies and advanced diagnostics

Establishing the treatment plan always starts with an accurate and timely diagnosis. Patients have access to state-of-the-art imaging technologies that allow accurate assessment of the extent of the disease.

In addition, the Institute offers advanced and sophisticated laboratory investigations, including molecular and genomic analyses, which are critical for identifying biological features of cancer and guiding therapeutic decisions

Minimally invasive surgical techniques and multidisciplinarity

When indicated, surgery is performed with minimally invasive techniques (laparoscopic or thoracoscopic), which reduce operative trauma, promote faster recovery, and improve postoperative quality of life. Every treatment choice is defined within the GIC, ensuring a consistent and integrated approach.

Clinical research and access to trials

As an IRCCS, the Candiolo Institute combines clinical practice with a strong vocation for scientific research. Patients can be evaluated forinclusion in active clinical trials, which represent a real chance to access innovative therapies not yet available in standard practice. Collaboration between care and research is a distinctive value that translates into concrete opportunities for the patient.

Care and support every step of the way

The Interdisciplinary Care Group takes care of the person at every stage: from diagnosis to treatment to follow-up, with attention to nutritional support, psychological health, and reintegration into daily life. The organization of checkups, visits and treatment is designed to ensure continuity and serenity, always valuing the human dimension of care.